“The dedicated life is the life worth living. You must give with your whole heart.”

Source: Attributed in posthumous publications, Einstein and the Poet (1983), p. 142

Source: I Know Why the Caged Bird Sings

Source: Peace Pilgrim: Her Life and Work in Her Own Words (1982), p. 95 (1994 edition)

1900s, Address at the Prize Day Exercises at Groton School (1904)
Context: Of course, the worst of all lives is the vicious life; the life of a man who becomes a positive addition to the forces of evil in a community. Next to that and when I am speaking to people who, by birth and training and standing, ought to amount to a great deal, I have a right to say only second to it in criminality comes the life of mere vapid ease, the ignoble life of a man who desires nothing from his years but that they shall be led with the least effort, the least trouble, the greatest amount of physical enjoyment or intellectual enjoyment of a mere dilettante type. The life that is worth living, and the only life that is worth living, is the life of effort, the life of effort to attain what is worth striving for.

William James, "Is Life Worth Living?," The Will to Believe and Other Essays in Popular Philosophy (1897).
Misattributed

"Is Life Worth Living?"
Variant: Believe that life is worth living, and your belief will help create the fact.
Source: 1890s, The Will to Believe and Other Essays in Popular Philosophy (1897)

Source: The Agony and the Ecstasy